4. [4 points] Stef and Mosta are writing problems for the final exam. The exam consists of 3 questions written by Stef and 2 questions written by Mosta. The time (in minutes) it takes a student to solve a question written by Stef is normally distributed with mean 20 and standard deviation 5, while the time it takes to solve a question written by Mosta is also normally distributed, but with mean 25 and standard deviation 15. Suppose the student randomly chooses a question on the exam and starts working on it, what is the probability that they solve the question within a 15-minute window?